1. Field of the Invention
The present invention relates to a power steering apparatus which includes a control valve for controlling the change-over of a working fluid passage with respect to a power cylinder.
2. Description of the Related Art
Conventionally, an engine speed sensitive type control valve 1 as shown in FIG. 10, or a vehicle speed sensitive type control valve 6 as shown in FIG. 11 have been used as a control valve of a power steering apparatus.
In the control valve 1 shown in FIG. 10, a rotary pool 1B is fitted into a sleeve 1A, and the rotary spool 1B and sleeve 1A are coaxially arranged so as to be relatively displaceable in accordance with a steering torque. The sleeve 1A is formed with a port group (four sets in FIG. 10). One set of the port group is composed of three ports, that is, a supply port 2 connected to a pump side supply passage, and a first port 3A and a second port 3B which are arranged on both sides of the supply port 2 and are connected individually to a first chamber and a second chamber of a power cylinder. The supply port 2 and first and second ports 3A and 3B are arranged around the central axis so as to be symmetrical with respect to the axial point. Moreover, the rotary spool 1B is formed with a plurality of return ports 4 (four in FIG. 10) which communicate with a tank side return passage and are arranged around the central axis so as to be symmetrical with respect to the axial point. The control valve 1 includes longitudinal grooves 5A to 5D. Longitudinal grooves 5A and 5B are formed at an inner surface of the sleeve 1A and at a position including the first port 3A and the second port 3B. A longitudinal groove 5C is formed at an outer surface of the rotary spool 1B and at a position relative to the supply port 2 of the sleeve 1A, and a longitudinal groove 5D is formed at the outer surface of the rotary spool 1B and at a position including the return port 4. These adjacent ports (supply port 2, first port 3A, second port 3B, return port 4) are capable of mutually communicated via these longitudinal grooves 5A to 5D.
In the control valve 1 shown in FIG. 10, in the case of neutral steering, a working fluid supplied to the supply port 2 flows from the longitudinal groove 5C to the return port 4 via the longitudinal grooves 5A, 5B and 5D. In the case of steering wheel turn, the working fluid supplied to the supply port 2 flows from the longitudinal groove SC to the first port 3A (or the second port 3B) via the longitudinal groove 5A (or 5B) which is correlated with a steering wheel turn direction, and then, is supplied to the first chamber (or the second chamber) of the power cylinder so as to assist a steering force. At that time, a high pressure is applied to a portion of the longitudinal groove 5A (or 5B) of the sleeve 1A.
In the control valve 6 shown in FIG. 11, the sleeve 1A is formed with a second supply port 7 connected to a pump side supply passage, in addition to the construction of the control valve 1 shown in FIG. 10. The control valve 6 includes the following longitudinal grooves 8A and 8B. longitudinal grooves 8A and 8B are formed at an inner surface of the sleeve 1A and arranged on the both sides of the second supply port 7, and a longitudinal groove 9 is formed at an outer surface of the rotary spool 1B and at a position relative to the second supply port 7 of the sleeve 1A. The adjacent second supply port 7 and return port 4 of the rotary spool 1B are capable of mutually communicated via these longitudinal grooves 9, 8A, 8B and 5D.
In the control valve 6 shown in FIG. 11, a working fluid force fed by a pump is supplied to only supply port 2 during low vehicle speed, and is supplied to both supply port 2 and second supply port 7 during high vehicle speed. The assist force is greater during low vehicle speed, and is reduced during high vehicle speed.
The aforesaid prior art has the following problems.
{circle around (1)} In the control valve 1 shown in FIG. 10, the sleeve 1A is formed with the longitudinal grooves 5A and 5B at its inner surface. Longitudinal grooves 5A and 5B are arranged in parallel with each other in a longitudinally wide range of the sleeve 1A with the same length. This makes rigidity of the sleeve 1A low (see FIG. 10B). In the sleeve 1A, an oil pressure applied to any longitudinal groves 5A and 5B becomes uniform in the case of neutral steering. The oil pressure elevates to a high pressure state in the case of a low vehicle speed. As a result, in the sleeve 1A, there is generated a diamond-shaped distortion such that a certain portion of these longitudinal grooves 5A and 5B are outwardly bulged (see FIG. 10C).
{circle around (2)} In the control valve 1 shown in FIG. 11, the sleeve 1A is formed with the longitudinal grooves 5A and 5B at its inner surface, and further, includes the longitudinal grooves 8A and 8B. These longitudinal grooves 5A and 5B and 8A and 8B are arranged in parallel with each other in a longitudinally wide range of the sleeve 1A with the same length. This makes rigidity of the sleeve 1A low (see FIG. 11B). In the sleeve 1A, a working fluid is supplied to only supply port 2 in the case of a low vehicle speed, and is not supplied to the second supply port 7. For this reason, pressure distribution acting to a circumferential direction of the sleeve 1A becomes unbalanced and distortion is generated in the sleeve 1A (see FIG. 11C).
{circle around (3)} In the prior art, the aforesaid distortion of the sleeve 1A stated in the above items {circle around (1)} and {circle around (2)} gives an influence to a relative rotation (ie., valve characteristic) of the sleeve 1A and the rotary spool 1B. In order to avoid the aforesaid influence, the clearance formed between the sleeve 1A and the rotary spool 1B is made large. However, this is a factor which increases oil leakage and lowers pump efficiency.
It is, therefore, an object of the preset invention to improve rigidity of a sleeve constituting a control valve, and to minimize a clearance formed between the sleeve and a rotary spool so as to reduce oil leakage while preferably securing operation of the sleeve and the rotary spool, and thus, to improve the valve characteristic.
According to the present invention, there is disposed a power steering apparatus including
a control valve for controlling a change-over of a pump side supply passage and a tank side return passage with respect to a first chamber and a second chamber of a power cylinder of a steering arrangement,
The control valve comprises a sleeve and a rotary spool fitted into the sleeve.
The sleeve and the rotary spool are coaxially arranged so as to be relatively displaceable in accordance with a steering torque.
The sleeve has a supply port connected to the pump side supply passage, and first and second ports which are connected individually to the first and second ambers of the power cylinder and are arranged around a central axis so as to be symmetrical with respect to an axial point.
The rotary spool has a return port which is connected to the tank side return passage and is arranged around a central axis so as to be symmetrical with respect to an axial point.
Upon assembling the sleeve and the rotary spool, each longitudinal groove extending in a valve axial direction is formed at an inner surface of the sleeve so that adjacent ports of the sleeve and the rotary spool communicate with each other. Each upper end of the adjacent longitudinal grooves is arranged in a stagger layout.
Furthermore, according to the present invention, there is disclosed a power steering apparatus including
a control valve for controlling a change-over of a pump side supply passage and a tank side return passage with respect to a first chamber and a second chamber of a power cylinder of a steering arrangement.
The control valve comprises a sleeve and a rotary spool fitted into the sleeve.
The sleeve and the rotary spool are coaxially arranged so as to be relatively displaceable in accordance with a steering torque.
The sleeve has a supply port connected to the pump side supply passage, and first and second ports which are connected individually to the first and second chambers of the power cylinder and are arranged around a central axis so as to be symmetric with respect to an axial point.
The rotary spool has a return port which is connected to the tank side return passage and is arranged around a central axis so as to be symmetrical with respect to an axial point.
Upon assembling the sleeve and the rotary spool, each longitudinal groove extending in a valve axle direction is formed at an inner surface of the sleeve so that adjacent ports of the sleeve and the rotary spool communicate with each other. Each lower end of the adjacent longitudinal grooves is arranged in a stagger layout.
Furthermore, according to the present invention, there is disclosed a power steering apparatus including
a control valve for controlling a change-over of a pump side supply passage and a tank side return passage with respect to a first chamber and a second chamber of a power cylinder of a steering arrangement,
The control valve comprises a sleeve and a rotary spool fitted into the sleeve.
The sleeve and the rotary spool are coaxially arranged so as to be relatively displaceable in accordance with a steering torque.
The sleeve has a supply port connected to the pump side supply passage, and first and second ports which are connected individually to the first and second chambers of the power cylinder and are arranged around a central axis so as to be symmetrical with respect to an axial point.
The rotary spool has a return port which is connected to the tank side return passage and is arranged around a central axis so as to be symmetrical with respect to an axial point,
Upon assembling the sleeve and the rotary spool, each longitudinal groove extending in a valve axial direction is formed at an inner surface of the sleeve so that adjacent ports of the sleeve and the rotary spool communicate with each other. Each upper end of the adjacent longitudinal grooves is arranged in a stagger layout, and each lower end thereof is arranged in a stagger layout.